1. Field of the Invention
This invention relates to Christmas tree lighting systems utilizing a plurality of strings of lights which can be separately actuated and specifically to a Christmas tree lighting control system that allows the brightness of each string of lights connected to it to change slowly in accordance with a user supplied manual adjustment. When light strings having different colored bulbs in each string are used the slow change in brightness or fading of each strings allows the controlled lights to give a special effect wherein the sequential actuation of successive differently colored light strings can slowly modify the color and appearance of the Christmas tree they are placed upon.
2. Description of the Related Art
It is well know to use decorative light sets having a plurality of separately actuatable strings of lights wherein a controller activates the various light strings either simultaneously or alternatively. Typically, the bulbs in each string are caused to cycle on and off in order to provide a more interesting appearance. However, often the sudden on/off action of the flashing lights gives an unduly harsh and unpleasant appearance especially when a whole string of multiple lights is flashed on and off. This problem is prevalent especially when the tree is not being admired but rather only the reflection of the light from the flashing lights is being perceived involuntarily in the same room. As is the case with any on and off light source, such a flashing stimulus might be distracting and generally unpleasant. Furthermore, because of the violent on/off action, the lamp filaments are thermally shocked This thermal shock comes from the repeated full power application and its inherent heat generation within the filament and subsequent rapid cool off of the filament during power off conditions. It is therefore desirable to have a fading effect associated with the operation of the lights so the transition from a full OFF to a full ON condition and from a full ON to a full OFF condition is more gradual.
The on/off and fading concepts of control of decorative lights in the prior art is exemplified by Ferrigno U.S. Pat. No. 3,793,531, issued Feb. 19, 1974, Weiner et al U.S. Pat. No. 4,215,277 issued July 29, 1980, Davis U.S. Pat. No. 4,678,926 issued July 7, 1987, Bartleucci et al U.S. Pat. Nos. 4,780,621 issued Oct. 25, 1988, and McNair U.S. Pat. No. 4,888,494 issued Dec. 19, 1989.
Ferrigno, U.S. Pat. No. 3,793,531, a proponent for fader operation of lights, describes a TRIAC activated power control system using a variable rate oscillator to determine the duration of the conduction angle of the TRIAC, thereby controlling the AC power level, or brightness of lights controlled therewith. The oscillator can be set for frequencies greater than, but close to 60Hz, the powerline frequency This produces a slow variation in average power to the load at a "beat" frequency equal to the difference between the power line frequency and that of the oscillator. The cycle time, or period between "full" brightness and "low" brightness operation is dependent on the difference between the power line frequency and that of the variable rate oscillator (col 5, line 58-65). Such a fading scheme requires that the variable rate oscillator be quite stable over time for the fading effect to be constant.
Weiner et al U.S. Pat. No. 4,215,277 discusses an on/off system that discloses a controller for sequentially energizing a plurality of light strings, e.g. Christmas tree light strings The controller is characterized by the use of a plurality of solid state switches or TRIACS, each TRIAC being connected in series between a 110 volt AC power supply and a light string comprised of multiple incandescent lamps. The TRIACS are controlled by a programmable ring counter which energizes the TRIACS in a determined sequence. The counter, in turn, is switched by clock pulses supplied by a variable oscillator at a rate which can be varied by the user. When the TRIAC is energized, i.e. on, it applies the 110 volt AC supply voltage to the light string connected thereto thus energizing all of the lamps on the string in an identical manner.
For example, assuming four lamps, L1-L4 as shown in FIGS. 4-7 of the '277 Patent, these lamps may be energized in a repeating sequence of L1, L2, L3 L4, L3, L2, etc., or in a repeating sequence of L1, L2, L3, L4, L1, L2, L3 etc. The FIG. 5 embodiment permits the sequence L1, L1 L2, L1 L2 L3, L1 L2 L3 L4, L1 L2 L3 L4, and OFF to be continuously repeated. Various other sequences are disclosed with respect to FIGS. 4-7. However, the '277 Patent does not disclose circuitry for producing a gradual intensity change for each light string, nor does it provide circuitry for producing an adjustable overlap between the energized light strings.
Davis, U.S. Pat. No. 4,678,926 describes generally a Christmas tree lighting control system wherein the light output of an internal light source is modulated by a mechanically rotated baffle having certain apertures to excite a set of photoelectric cells. The photoelectric cells in turn modulate the operation of the TRIAC based power control units that activate each individual light string.
The control circuitry disclosed in the '926 Patent includes an electro-mechanical assembly (see FIG. 2) having a motor 11 which slowly turns a patterned baffle 27 to expose, at predetermined time intervals, four photocells 30 positioned behind the rotating baffle 27 to light from lamp 12. The varying output from each of the photocells 30 controls duty cycle units 17-20 to change output power in accordance with the output of their respective photocells 30. The output of the duty cycle units controls strings of ornamental lights which are connected to conductor cord 9. As baffle 27 rotates, the light strings are controlled in intensity and duration in proportion to the photocell output.
Bartleucci et al U.S. Pat. No. 4,780,621 describes a means for controlling low voltage light emitting diodes (LED's) to achieve an on/off flashing effect. A counter divider is included in the controlling means having multiple binary stages, i.e. an output every 2, 4, 8 or 16 pulses from an oscillator operating between 20 and 130 Hz. (col 3, line 41). Because the oscillator output can be divided by the counter divider by a factor of 2, 4, 8 or 16, the effective frequency available to drive the TRIACS, assuming an input of 120 Hz, is 60, 30, 15 and 71/2 Hz. Therefore the fixed intensities of the lamps controlled by the TRIACS will be in the ratio of 1, 1/2, 1/4 and 1/8 respectively.
Each set of lamps is comprised of light emitting diodes (LEDs) LEDs of different color are connected in two parallel groups with opposite polarity on the same string, with the light string being energized by a TRIAC. Various effects may be obtained depending upon the specific gating of the TRIACs. For example, if the TRIAC is gated on only during the positive half cycle of the alternating current (AC) energizing voltage, only one of the two groups of LED's will be energized to emit light. Alternatively, if the TRIAC is gated on only during the negative half cycle of the AC voltage, then only the second group of LEDs will turn on. Thus, the string of LEDs may be energized to first blink green, then blink red. As the on-state of the triac shifts relative to the AC voltage, the energization of the first and second LED groups will vary to gradually change color.
FIG. 4 of the '621 Patent shows the TRIAC gating pulses (Output "A"), in various phase relationships to the 60 Hz voltage. As the phase relationship changes, the light string goes from a starting condition in which LED1 is on and LED2 is off, to an intermediate condition where both LEDs are on at full intensity, to a condition where LED1 is off and LED2 is on, and so on. The '621 Patent also discloses the use of a tri-color light emitting diode to produce light which appears to gradually drift from a first color to a second color to a third color (See Col. 5, lines 47 et seq.). The circuitry disclosed and claimed in the '621 Patent is limited to utilizing the non-linear operating characteristics of LEDs, and could not be utilized in the same manner with conventional incandescent lamps.
McNair, U.S. Pat. No. 4,888,494, again an example of ON/OFF light operation, describes an electromechanical switching device where either a first or second electrical load is switched in on/off fashion in response to mechanical cam motion. The rate of the cam rotation can be controlled manually.
The above art generally discusses means for on/off or fading activation of strings of lights by the use of TRIAC control or regular mechanical switches. One aspect of the art related to the fading of lights that poses a challenge is the high stability requirement of some of the techniques using an oscillator near the power line frequency to interact with the powerline frequency to control the state of illumination of the lights, as in Ferrigno. This interaction between the external oscillator and the power line has to be stable over time to achieve a predictable fading effect. The high stability requirement implies that the parts used for the oscillator must be of relatively high cost.
It is, therefore, an object of the present invention to provide an improved, stable, cost effective Christmas tree lighting control which when in operation will ramp the brightness of a string of lights up and down in a repeatable and stable fashion over a period of tens of seconds, thereby allowing the appreciation of sequential illumination of multi-colored strings of lights on a pleasant level without the discontinuities present in a harsh on and off flashing system.
Another object of the present invention is to provide a Christmas tree lighting system wherein the lights are not shocked thermally by violent, nearly instantaneous on/off operation but rather subjected to a slow, continuous increasing and decreasing power level that extends the heating and cooling cycle of each individual lamp over many seconds. This reduced rate of rise in temperature extends the operating life of the lamps by reducing the effects of thermal cycling.
It is a further object of the present invention to provide a light string control system which can readily vary the overlap between activation of the various light strings with respect to other strings of lights in the system.
It is still a further object of the present invention to provide a control unit which can be used with separate strings of conventional lights to obtain the gradual control of illumination of the light strings, thereby giving the appearance of fading overlap of the various strings.
It is yet another object of the present invention to provide an integral control unit permanently coupled to multiple light strings to control their fading characteristics.
Yet another object of the invention is to provide a separate conveniently packaged control unit with standardized sockets to allow connection of several light strings thereto.